This invention relates to electrochemical battery cells, particularly alkaline cells containing copper oxide as an active cathode material.
Copper oxides have been used as positive electrode active materials in electrochemical battery cells for many years. For example, copper oxide, particularly copper (II) oxide, CuO, was the active material in wet cell railway batteries, such as those described by George W. Heise and N. Corey Cahoon (eds.), The Primary Battery, John Wiley & Sons, New York, 1971, Vol. 1, Chapter 4, pp. 192-205. Copper oxides have also been used as active materials in dry cell batteries with aqueous and nonaqueous electrolytes. Examples include dry cell alkaline batteries with zinc as the negative electrode active material, and nonaqueous batteries with lithium as the negative electrode active material. Copper oxide cell designs have included button and cylindrical cell shapes and flat, bobbin and spirally wound electrode configurations. An advantage of copper oxide as an active positive electrode material is its high density compared to other commonly used materials, such as manganese dioxide. As disclosed by Davis et al. in U.S. Pat. No. 6,489,056, issued Dec. 3, 2002, CuO may also be advantageous as a replacement for electrolytic manganese dioxide (EMD) in alkaline cells that have a zinc anode free of lead, mercury, or cadmium, since CuO can more quickly absorb hydrogen generated in the anode than EMD at high temperature.
When alkaline Zn/CuO cells are discharged, CuO is reduced to metallic copper. In some cases a distinct step has been observed between two voltage plateaus in the voltage vs. time discharge curve for CuO, while in others the discharge curve has a single voltage plateau. The presence of two voltage plateaus suggests that the discharge may involve the reduction of both CuO and Cu2O, with the higher plateau (about 1.05-1.1 volts) corresponding with the reduction of CuO, and the lower plateau (about 0.85-0.88 volt) corresponding with a reduction of Cu2O. The discharge mechanism is very complex and not fully understood.
Regardless of the mechanism, conventional Zn/CuO cells operate almost entirely at the same low voltage as a Zn/Cu2O cell. When two plateaus have been observed, the first one tends to be short in duration. Though the total cell capacity may be high, most of that capacity is delivered at a low voltage. This low voltage may be too low to even operate some devices designed to use “1.5 volt” Zn/MnO2 batteries. Devices with lower operating voltages might operate for a time using alkaline Zn/CuO batteries made according to the prior art, but that time may be too short for such Zn/CuO batteries to be considered as practical replacements for alkaline Zn/MnO2 batteries.
In view of the above, an object of the present invention is to provide a high capacity electrochemical battery cell with a copper oxide positive electrode.
Another object of the present invention is to provide an electrochemical battery cell that is able to deliver improved capacity when discharged to a high voltage endpoint.
Another object of the present invention is to provide a copper oxide electrochemical battery cell with improved discharge characteristics that is economical to produce.